1. Field of the Invention
This invention relates generally to unwind machines of the type adapted to deliver a paper web from a paper roll to a utilization device such as a laser printer, and to accommodate abrupt changes in the speed of the paper web in the laser printer.
2. Description of Prior Art
In order to accommodate the wide range of speed changes that a laser printer requires, unwind machines feed the paper web into the laser printer from a roll of paper web material and a free loop of the web material is provided between the laser printer and the paper roll. The paper roll is unwound by a driven belt or roller, which is driven at a variable speed in response to the output signal from an ultrasonic sensor that provides an indication of the depth of the free loop of the paper web. The free loop is formed between a driven roller and an idler roller provided one on each side of this free loop. The speed of the belt which unwinds the paper web from the roll is varied in direct proportion to the input provided from an ultrasonic or photocell type sensor in accordance with known control systems generally. The reader is referred to Waddington U.S. Pat. No. 4,484,655 and Meschi U.S. Pat. No. 5,234,146. for a more complete description of such prior art systems.
Present day laser printers require such a wide range of speed changes that unwind systems such as that described above have difficulty in accommodating the speed changes of the paper roll that must be accommodated. That is, the paper roll has considerable inertia, and once rotated at a particular speed requires considerable braking by, or acceleration of, the driven roller or belt that may be beyond the capabilities of present day unwind machines. There is a need for reducing the abrupt speed changes at the unwind roll itself when the laser printer either stops the paper web or in some cases, actually reverses the direction of its movement.